Sister is a switch of name for the lovely new film by Swiss director Ursula Meier (Home), whose original French title, L’Enfant d’en haut, translates roughly as “The Kid From Up Above”. Said kid is Simon (Kacey Mottet Klein), a 12-year-old kleptomaniac who earns his crust stealing equipment from an Alpine ski resort.

The implications of “en haut” aren’t just topographical but also ones of class. The wealthy types up there, Simon claims, can’t care overly about their purloined stuff, because they instantly pay to replace it. We needn’t agree, of course: Meier withholds judgment, merely filling us in bit by bit on the hard-knock life Simon has been forced to live.

Taking the cable-car back down the mountain to where he stays with his broke, promiscuous and generally bedraggled sister Louise (Léa Seydoux), Simon is very much the breadwinner, selling stolen gloves and shades to other local kids for pocket money and trying to get the best price on the high-end skis he’s also managed to waddle off with.

The milieu provides a built-in disguise: wearing wraparound googles and head-to-toe outdoorwear, he’s a miniature Raffles in polyester. He cajoles his way in everywhere, and we needn’t trust the story he tells about the death of his parents in a car crash, but he’s also a bright spark, hard to dislike, and hugely vulnerable beneath it all.

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In a year set to be studded with great child acting – think Quvenzhané Wallis (Beasts of the Southern Wild) and Tom Holland (The Impossible) – it would be a mistake to neglect Klein, who’s a marvel of puckish naturalism throughout this. Seydoux, too, does capable work as a scrounging sexpot in tight jeans, building a boisterous but fraught relationship with her co-star that keeps revealing unexpected layers.

It perhaps sounds a little like a Dardennes brothers film – last year’s The Kid with a Bike comes readily to mind. But it outshines that one, because a healthy seam of mischief helps cut through the occasionally rote social comment. Meier, working with the great French cinematographer Agnès Godard (Beau Travail), finds a lonely quality in the thin mountain air, a climate that thrill-seekers inhale and evacuate to leave this invisible boy behind, converting their blessings into his loot.